Orion XT12 - Manual (Page 11)

Preparing the Telescope for Collimating
Once you get the hang of collimating, you will be able to do it
quickly even in the dark.
For now, it is best to collimate in daylight, preferably in a
brightly lit room and aimed at a white wall. It is recommended
that the telescope tube be oriented horizontally. This will pre-
vent any parts from the secondary mirror from falling down
onto the primary mirror and causing damage, should some-
thing come loose when you are making adjustments. Place
a sheet of white paper inside the optical tube directly oppo-
site the focuser. This will provide a bright “background” when
viewing into the focuser. When properly set up for collimation,
your telescope should resemble Figure 22.
Aligning the Secondary Mirror
With the collimation cap in place, look through the hole in the
cap at the secondary (diagonal) mirror. Ignore the reflections
for the time being. The secondary mirror itself should be cen-
tered in the focuser drawtube, in the direction parallel to the
length of the telescope. If it isn’t, as in Figure 21b, it must be
adjusted. This adjustment will rarely, if ever need to be done.
Using a 2mm hex key, loosen the three small alignment
set screws in the center hub of the 4-vaned spider several
turns. Now keep the mirror’s holder stationary (be careful not
to touch the surface of the mirrors), while turning the cen-
ter screw with a Phillips head screwdriver (see Figure 23).
Turning the screw clockwise will move the secondary mirror
toward the front opening of the optical tube, while turning
the screw counter-clockwise will move the secondary mirror
toward the primary mirror.
Note: When making these adjustments, be careful not to
stress the spider vanes or they may bend.
When the secondary mirror is centered in the focuser draw-
tube, rotate the secondary mirror holder until the reflection of
the primary mirror is as centered in the secondary mirror as
possible. It may not be perfectly centered, but that is OK. Now
tighten the three small alignment screws equally to secure the
secondary mirror in that position.
If the entire primary mirror reflection is not visible in the sec-
ondary mirror, as in Figure 21c, you will need to adjust the tilt
of the secondary mirror. This is done by alternately loosen-
ing one of the three alignment set screws while tightening the
other two, as depicted in Figure 24. Do not make excessive
turns of these set screws or force them past their normal trav-
el. A simple 1/2 turn of the screw can dramatically change the
tilt of the mirror. The goal is to center the primary mirror reflec-
tion in the secondary mirror, as in Figure 21d. Don’t worry that
the reflection of the secondary mirror (the smallest circle, with
the collimation cap “dot” in the center) is off-center. You will fix
that in the next step.
11
Figure 22. The SkyQuest
IntelliScope properly set up
for collimation. Note the
white paper placed across
from the focuser, and the
level angle of the optical
tube. Ideally, the telescope
should be pointing at a
white wall.
Figure 23. To center the secondary mirror under the focuser, hold
the mirror holder in place with one hand while adjusting the center
bolt with a Phillips screwdriver. Do not touch the mirror’s surface!
Figure 24. Adjust the tilt of the secondary mirror by loosening or
tightening the three alignment set screws with a 2mm hex key.